The objective of this work is to analyze the property changes of oxide ceramic fibers when they are exposed to elevated temperatures. Oxide fibers are used as reinforcements on ceramic matrix composites; materials that show high strength and considerable toughness. However, these fibers are susceptible to strength loss due to grain growth when exposed to temperatures exceeding 1000°C. This is an important issue since these temperatures are easily reached during the lifetime of the fibers, e.g. during composite processing or in-field application. Therefore, the mechanical properties and microstructure of Nextel 610 fibers were characterized before and after the production of minicomposites. Three different matrix compositions were used (alumina, alumina+zirconia, mullite+zirconia) in order to see the influence of the matrix composition on the microstructure evolution of the fibers. Sintering temperatures of 1200 and 1300°C for 2 h were used to consolidate the matrices. For comparison, fibers alone were also tested after heat treatments simulating the composite sintering. The minicomposites sintered at 1200°C showed a higher strength due to the lower degradation of the fibers. In this matter, fibers that were embedded on matrices containing mullite showed the lowest grain growth. Still, the final strength of the minicomposites was dependent on the fiber degradation and matrix consolidation.